undending <br>'s

Ok here's my problem. I have idiots on my forums who are, for the sole purpose of being annoying, posting messages like

thats cool

{insert about 150 newlines}

not

i'm not very good with regular expressions, and i was wondering if anyone could help me turn the aforementioned 150 new lines (give or take) into 2 (ie. a new paragraph).

i guess in the censor text function i could try something like

$message=ereg_replace("\n[\n]+","\n\n",$message);

before \n is changed to <br> right?